Eur. Phys. J. E (2016) 39: 120
https://doi.org/10.1140/epje/i2016-16120-8

Regular Article

Confinement effect on the dynamics of non-equilibrium concentration fluctuations far from the onset of convection

¹ Laboratoire des Fluides Complexes et leurs Réservoirs - UMR5150, Université de Pau et des Pays de l’Adour, 1 Allée du Parc Montaury, 64600, Anglet, France
² Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander-Universität, 91052, Erlangen, Germany
³ Courant Institute of Mathematical Sciences, New York University, 10012, New York, NY, USA
⁴ Departamento de Fısica Aplicada I, Facultad de Fısica, Universidad Complutense, 28040, Madrid, Spain
⁵ Centre National d’Études Spatiales (CNES) 2, Place Maurice Quentin, 75001, Paris, France

^* e-mail: fabrizio.croccolo@univ-pau.fr

Received: 16 November 2016
Accepted: 18 November 2016
Published online: 12 December 2016

Abstract

In a recent letter (C. Giraudet et al., EPL 111, 60013 (2015)) we reported preliminary data showing evidence of a slowing-down of non-equilibrium fluctuations of the concentration in thermodiffusion experiments on a binary mixture of miscible fluids. The reason for this slowing-down was attributed to the effect of confinement. Such tentative explanation is here experimentally corroborated by new measurements and theoretically substantiated by studying analytically and numerically the relevant fluctuating hydrodynamics equations. In the new experiments presented here, the magnitude of the temperature gradient is changed, confirming that the system is controlled solely by the solutal Rayleigh number, and that the slowing-down is dominated by a combined effect of the driving force of buoyancy, the dissipating force of diffusion and the confinement provided by the vertical extension of the sample cell. Moreover, a compact phenomenological interpolating formula is proposed for easy analysis of experimental results.